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flyinchips
04-22-2005, 04:06 PM
I am attempting to machine some A2 tool steel with a Shop Task 3 in 1 machine. I am using a 1/2 TiN 4 flute cutter. The recommendation for feed and speed are 2.7 IPM and 230 RPM. This produces a .003 chip load and requires .5 Hp. I am attempting a .1 x .09 cut that is (I think) bellow the recommended max for this size cutter (.125 x .125). I have set the speed to 460 RPM and feed at 2 IPM, (.001 chip load and .33 HP), because with a fresh cutter, this produced good results for about 20 inches, but I am still having cutting troubles to the tune of 3 worn/broken cutters and the fourth is now chattering when I start a cut, but is OK mid cut. I have the gib screws tight to the point where the CNC system is just, reliably, capable of moving the carriages.

Does anybody have a cutting recommendation for this configuration? I'm looking for a general guideline or experiences here. I'm using Kool Mist 77 as the coolant. The chips look right, but I'm killing cutters! Should I back waay of the on the feed to less than 1 IPM and endure the wait for this job to be done?

My Chips aren't Flying today......

J Tiers
04-22-2005, 04:16 PM
Well, I'm no expert, but whenever I have cutter trouble, I try slowing down the cutter and taking more chip load. That usually works, particularly with tool steels.

On that subject, IIRC tool steels run around 40 FPM cutter speed, sometimes less. Your 460 RPM is about 60 FPM. Odds are that your faster speed and low feed per tooth are just work or heat hardening the material and burning up cutters.

I have found a huge difference between 60 and 35 FPM in tool steel (in my case, O1).

precisionworks
04-22-2005, 04:46 PM
JT hit it. Not enough chip load & SFM too high. If I were doing this job, a solid carbide end mill would be my first choice for A2. You'll gain decreased tool deflection and longer cutting time before dulling.

(I usually buy five at a time, resharps on eBay, about $4 - $5 each.)

------------------
Barry Milton

flyinchips
04-22-2005, 05:00 PM
I started at 230 RPM and 2 IPM, about 30 FPM and went up incrementally 230, 280, 320, 360, 420, 460, because the machine wasn't happy at 230. It seemed happier removing smaller chips faster. 460 was too fast so, I settled for 420.

The recommended range for this material is 30 to 60 FPM.

Derek13
04-22-2005, 05:19 PM
the reccommended sfpm's given are just that.. reccomended... many variables have to be considered, including rigitity, size of machine, cutter, etc... the sfpm's are just a starting point.

SGW
04-23-2005, 07:49 AM
If you're using ElCheapo end mills, that may be part of the problem. It may be worth your while to pay the bucks for a Niagara, Weldon, etc. end mill and see if that lasts any better. Note that TiN coating, by itself, will not salvage a poor-quality end mill.

(If you're already using a top-quality end mill, forget I said anything....)

JCD
04-23-2005, 10:30 AM
A2 has a tendency to work harden, be sure that once you begin your feed, don’t stop until the cutter in out of the work piece. A higher cobalt content cutter might help. Carpenter makes a “free machining” A2.

JCD

3 Phase Lightbulb
04-23-2005, 11:52 AM
My Speeds and Feeds table:

Cow Burger: 4 bites per minute (heavy cut).
Fries: 12-14 bites per minute (light cuts).
Coke: 12 oz per minute (light volumes)

Check out (Appendix A: Tables) in this online machine shop manual. Lots of usefull tables including speeds and feeds for drilling and milling with most materials:

http://www.bbssystem.com/downloads/machine-shop/appa.pdf

The complete manual is available online here:

http://www.bbssystem.com/viewtopic.php?t=22

-Adrian

flyinchips
04-25-2005, 08:31 PM
You're a smart bunch!

After reviewing your comments, I went back to square one and convinced my self that the recommended settings were good, my cutter was not "el cheapo", so it had to be too much for my little machine to cut. I reduced the cut thickness from .09 to .05 and everything is great! No more chatter, broken bits and the job is done.

I guess the moral of the story is: Don't ask a little machine to do what a big machine can does.


Thanks!